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C++

Archived

This page has been archived and will receive no further updates.

See:

Libraries​

C++ Standard Library​

Note: The C++ Standard Library/stdlib is often called "STL." This is inaccurate, but is noted here so it can be recognized (http://stackoverflow.com/a/5205571/399105)

Boost​

Besides the standard library, Boost is a collection of incredibly useful C++ libraries.

Install Boost on Ubuntu:

sudo apt install libboost-all-dev

Or search for the particular boost package needed:

apt-cache search libboost

OOP​

Also see: Object-oriented programming (OOP)

Objects created using the new keyword must be deleted when you're done using them using the delete keyword

Creating objects​

There are two ways to create objects in C++ (heap memory can also be allocated in C using malloc() and must be freed using free()):

  1. Create the object on the stack/static storage:

    std::string str;
    • Must know the exact quantity, lifetime, and type of objects
    • The compiler determines how long the object lasts and can automatically destroy it.

  2. Create the object on the heap by using the new keyword

    std::string* str = new std::string();
    • Uses:
      • When you need a variable to exist outside of its local scope (after the current function returns)
      • Use the heap when creating large objects or a large number of objects since stack space is limited. This may include a variable created within a recursive function if it is recursively invoked too many times.
      • Each thread has its own stack but shares the same heap
    • When using the new keyword, you get back a pointer
    • The programmer must determine programmatically when to destroy the object, and then perform the destruction using the delete keyword. A better way to handle this is to use a smart pointer (like std::tr1::unique_ptr, boost::scoped_ptr, boost::shared_ptr), which will take care of safely destroying the object when it's no longer in use: 
      boost::scoped_ptr<pipe> sp(new pipe);
      http://stackoverflow.com/a/395519/399105
    • Storage is managed dynamically at runtime
    • Amount of time required to allocate storage on the heap is significantly longer than the time to create storage on the stack
    • Third-party garbage collectors exist for C++ that automatically discover when an object is no longer in use and destroy it.

Access control​

These are placed in the header files

  • Private (default for classes)
  • Public (default for structs)
  • Protected

Friend keyword​

Used to give access to all or part of a private class to another class.

Virtual functions​

Functions in a base class must be declared as virtual so inherited classes can use their own overridden functions when upcasting.

Misc​

Other differences from C​

  • In C, a function declaration with an empty argument list means that function can have any number of arguments, but in C++ it means it has no arguments: 
    int func2();
  • C++ introduces // comments; C doesn't have them
  • C++ has bool types, as well as true and false keywords. C doesn't.
  • In C, variables must be declared at the beginning of the scope, but in C++ they can be declared/defined at any point in the scope.